The good side of microbes goes under the microscope this week as we explore how the 100 trillion bacteria that thrive on us and in us, and even outnumber our own cells ten times over, work with the body to maintain good health. We also hear from the Nobel prizewinner who's turning the stomach bug Helicobacter pylori into an edible vaccine against the flu and how to build better bioreactors to culture them in! Plus, how trees cause clouds to form, more evidence that the building blocks of life came from outer space, how nicotine keeps smokers thin and built-in cardiac stem cells that can mend a broken heart...